Current large square balers are equipped with a plurality of pivotally mounted, upwardly biased twine tensioner arms, sometimes called slack take-up arms, respectively associated with a plurality of knotter assemblies (each knotter assembly described hereinafter is a double-tie knotter assembly) to maintain proper tension on the twine to ensure each knotter assembly performs properly. If the twine tensioner arm fails to maintain proper tension on the twine, the twine can be pulled out of the knotter assembly and a mistie occurs.
As a bale is being formed, the twine tensioner arms normally rotate approximately 30° from an initial extreme upper position to a lower extreme position. At the ending of the bale formation process, each twine tensioner arm should be located at the lowermost extreme position, and when the bale is complete and a knot has been sucessfully tied, each tensioner arm should return to the uppermost extreme position. If any of the tensioner arms are at either of these positions any time other than at the beginning or ending of the bale tying cycle, it indicates that something failed and a mistie has occurred.
Various tie monitoring devices have been designed for determining whether or not a mistie has occurred. For example, U.S. Pat. No. 4,765,235 discloses a tie monitoring device comprising upper and lower sensing rods which respectively extend horizontally above and below the tensioner arms of all of the knotters, with each of the rods having opposite ends carried by a pivotally mounted arm. Gravity maintains the upper rod in contact with the tops of the tensioner arms and a spring is coupled to each of the lower rod carrying arms so as to bias the lower rod upwardly into contact with the bottoms of the tensioner arms. Magnets are respectively carried at the outer end of one of the arms carrying the upper rod and at the outer end of one of the arms carrying the lower rod, with upper and lower sensors being mounted on the frame so as to register with these magnets to create a signal for being processed by a microprocessor only when the tensioner arms are in their extreme upper or lower positions. If the microprocessor determines that the signal received is at a time other than normal, a visual display within the tractor cab is activated to show a check knotter notation and an audible alarm is sounded. This patented design has the drawback that there is no way to determine which knotter has mistied since, due to the operation of the upper and lower rods, only one signal is generated to indicate a mistie at the beginning of the formation of a bale and only one signal is generated to indicate a mistie at the end of the formation of a bale.
Another microprocessor based mistie monitor or detector which does indicate to an operator which knotter has failed is disclosed in U.S. Pat. No. 4,753,463 (this mistie detector is associated with a different and more complex tensioner arm arrangement which is disclosed in U.S. Pat. No. 4,753,464) which provides switches located in the tying apparatus at such locations that they provide signals which can be processed so as to give an operator a first indication if a given knotter does not cycle and a second indication if a given knotter fails to tie a knot. This patented design has the drawbacks that: (a) the tensioner arm arrangements are relatively complex; and (b) the operator is not apprised of the relative positions of the tensioner arms one to another during the course of each tying cycle, resulting in the operator not having sufficient information from which to earlier detect or diagnose a pending mistie failure.
U.S. Pat. No. 4,196,661 discloses a mechanical mistie monitoring arrangement comprising a plurality of flags respectively mounted to the plurality of tensioner arms for moving up and down with the tensioner arms so that an operator can determine the relative position of one tensioner arm to another during a tying cycle. However, this arrangement has the drawbacks that: (a) the operator is required to look rearward to see the flags, thus distracting the operator and interfering with the operator's attention to other important operations; and (b) the operator's view is obstructed by such things as a dirty cab window and/or a cloud of dust as is often generated by the baler during baling operation. In another embodiment, a plurality of switches are respectively associated with the tensioner arms and are located so as to be closed and activate an alarm in the event that the tensioner arms move to a position indicating a mistie has occurred.
What is needed then is a microprocessor based tensioning arm position monitoring arrangement which senses the positions of the tensioner arms as they move between upper and lower extreme positions and which provides an in-cab display of individual tensioner arm positions during tying cycles and which uses this information to foresee misties, and/or determine that tensioner mechanisms are not set correctly, as well as determine when misties have already taken place.